Development And Test Of Intelligent Variable Spraying System For Large-load Plant Protection UAV

In recent years,China’s agricultural aviation plant protection industry has developed rapidly,and plant protection drones are widely used in China.As a new type of plant protection operation method,compared with ground machinery and manual spraying,plant protection drones not only have high operation efficiency and fast spraying speed,but also can solve the advantages of difficult ground machinery under complex plots.Due to the short development history of plant protection drones,there are still problems such as insufficient integration of agricultural machinery and agronomy,limited load,and short single operation time.Most of them use fixed spray width and fixed flow spraying,which can adapt to multiple planting modes and improve variable application.The utilization rate of pesticides and the improvement of spraying uniformity still need to be improved.In response to the above problems,this topic developed a three-layer centrifugal variable spray nozzle,with the pulse width modulation technology(Pulse Width Modula,PWM)as the core,combined with the embedded intelligent control technology to develop a set of plant protection UAV intelligent variable spray width,variable flow spraying system,which can effectively improve the poor integration of agricultural machinery and agronomy in the application of UAV plant protection,the inability of the sprinkler system to achieve variable spraying,and the impact of changes in sprinkler pressure on the atomization effect of sprinklers,etc.The indicators at all levels provide theoretical support and technical promotion basis for the continuous promotion and improvement of plant protection drones.The main research work and conclusions of this topic are summarized as follows.(1)Aiming at the problems of poor agricultural machinery and agronomic integration in the application of UAV plant protection,the inability of the sprinkler system to achieve variable spraying,and the change of sprinkler pressure affecting the spraying effect of the sprinkler,on the basis of in-depth research on the variable spraying method,according to the overall technical requirements of the variable spraying system,taking the large-load plant protection drone as the application object a set of intelligent variable spray width and variable flow spraying system for plant protection drones has been developed.The system includes a three-layer centrifugal variable nozzle and a variable spray boom.Combined with embedded intelligent control technology,4-level flow adjustment can be performed according to the degree of pests,diseases and weeds in the target operation area,and at the same time,according to the planting mode of different crops in the orchard,the droplet size and effective spray width can be adjusted to meet the needs of plant protection drones.The need for precise variable spraying.(2)Aiming at the problem that the existing aviation nozzles are easily affected by system pressure changes in terms of droplet size and uniformity of droplet distribution a three-layer centrifugal variable nozzle is developed,which can be used without changing the supply flow of the pump to achieve 4-level adjustment of the spraying flow,covering the basic disease level when the disease broke out,and improving the atomization effect of the nozzle when the system pressure changes.The microcomputer-controlled nozzle comprehensive performance precision test bench and the laser particle size analyzer were used to conduct indoor verification tests on the uniformity of droplet distribution under different pressures and the droplet size at different rotational speeds.The test results show that:when the system pressure changes,the coefficient of variation of the nozzle first decreased and then increased.The smallest coefficient of variation of the nozzle at 0.3MPa was 34.1%,and the uniformity of droplet distribution was the best.The particle size of the nozzle was negatively correlated with the rotational speed.When the 4-level flow adjustment is performed,the uniformity of droplet distribution varies within 5%,the coefficient of variation of droplet size is 1.1%,and the droplet size remains basically unchanged.(3)The developed variable spraying system was integrated into the large-load plant protection UAV,and field verification experiments were carried out.The effective spray width of the plant protection drone at the same height is calibrated,and the effective spray width of the aircraft can be changed between 2-5m.When the 4-level spraying rate is adjusted,the droplet density is 16.9,32.9,42.3,62.8/cm~2,the droplet size variation coefficient is 1.4%,affected by the outdoor environment compared with the indoor test and the test is slightly increased.The test proves that the system can realize 4-level adjustment of the spraying flow without changing the supply flow of the pump.Therefore,the variable spray system can improve the uniformity of droplet distribution and the change of droplet size caused by changes in system pressure.