Research On Orchard Target On-Line Probing Method And Air-Blast Variable Spraying Technology

At present orchard plant diseases and insect pests are mainly controlled by chemical pesticides. Spraying excessive amounts of pesticides will cause its large residues, which has seriously polluted ecological environment and fruit production. Target-oriented spraying is one of good means to reduce pesticide residues. The aim of the paper is to solve target-oriented spraying technical problem through studying targets online detection chemical pesticide variable spraying method. The main research contents and conclusions are the following four parts.(1) Orchard spray target profile probing method based on ultrasonic sensors was put forward. The precision analysis of the method at low speed condition was carried out, and the detection influence by sprayer speed was researched. In order to research on spray target profile probing method, and provide the theoretical support for variable spray based on real-time probing target profile, a tree spray target profile probing platform was improved. The platform was used in probing canopy profile of man-made tree with standard shape, cherry tree in the flowering stage and Hawthorn tree. Experiments indicate that measurement accuracy of standard shape canopy, cherry tree and Hawthorn tree canopy profile probing is92.8%,90.0%and87%, which shows that this method has high accuracy at the condition of low speed. The results of target detection speed influence test show that the target profiles detected at different speed are almost the same with lag phenomenon. The higher speed will cause the more lag. When the speed is not more than1m/s, the relationship between the lag distance and the speed is approximately linear. The straight-line equation obtained is d=0.117v-0.02, where d is the lag distance in m, v is the speed in m/s.The equation has a high fitting accuracy, where R2=0.983.(2) Orchard young tree target detection method was put forward, and the detection system was designed. Young tree target is hard to detect in orchard spraying because the tree canopies are small and sparse. In order to solve the problem, a young tree target detector which percept the target though probing orchard tree trunk was designed based on infrared sensors. Spraying parameters, such as spraying width and delay distance, could be input to the detector easily. Laboratory experiments indicated that accuracy of the detector is hardly affected by probing distance and diameter of tree-truck, while it is affected by the speed of sprayer a little. When the trunk is in the detection range of infrared sensor, and the speed is not more than1m/s, the calculating accuracy of spraying width is not less than96.1%. Orchard experiments showed that the probing accuracy of the detector is100%, when the speed of sprayer is not more than0.94m/s.(3) Nozzle flow models of PWM variable-rate spraying were studied and established. Nozzle flow model is indispensable in variable-rate spraying control based on Pulse Width Modulation (PWM) technology, especially when nozzles are controlled independently. Nozzle flow is affected by spraying pressure, PWM frequency and PWM duty cycle. It is hard to establish the model with a few trials. The central composite orthogonal regression tests were completed, and the flow models of TEEJET AITXA nozzles of type8002、8003and8004were obtained. The results of equation hypothesis test and test for lack of fit of flow models for regular pressure variable-rate spraying show that the three flow models are agreeable. The maximum relative error of the TEEJET AITXA nozzle model of type8002is7.05%, while the minimum relative error is0.14%. For the type8003, the maximum and minimum relative errors are7.27%and0.31%. And for the type8004, the maximum and minimum relative errors are7.94%and0.71%. Nozzle flow model validation trials show that the relative errors between model flow and actual flow are small. Nozzle flow model for high pressure variable-rate spraying is also established. The results from equation hypothesis test and test for lack of fit of flow model shows that those three flow models work well. Nozzle flow model validation trials show that the relative errors of model flow and actual flow are small, while the maximum and minimum relative error is6.50%and0.44%. The flows characteristics of different nozzles with the same type are almost the same.(4) Air-blast spraying atomization characteristics and spray nozzle droplets sedimentary characteristics were experimentally researched. A atomization characteristics test bench of air-assisted spraying was designed, with which the atomization effect impact characteristics of spraying pressure, wind speed, PWM frequency and duty cycle were studied. Experiments show that droplet size changes regularly as spraying pressure increases, and the average rates of change of the three statistics items commonly usedD43and Dv0.5are-90.33μm/MPa、-232.3μm/MPa and-300.2μm/MPa. When spraying pressure increases from0.2MPa to0.5MPa, D32, D43and.Dv0.5decrease by31%,36%and56%. Droplet size increases firstly then decreases as PWM frequency increases. When PWM frequency increases from2Hz to10Hz, D32, D43and DV0.5decreased by18%,31%and62%.Droplet size decreases as PWM duty cycle increases. When PWM duty cycle increases from30%to90%, D32, D43and Dv0.5decreased by19%,21%and27%. Droplet size changes regularly as wind speed increases, and the average rates of change of D32、D43and Dv0.5are2.62μm·s/m,3.59μm-s/m and6.83μm·s/m.When wind speed increases from3m/s to15m/s, D32, D43and Dv0.5decreased by46%,26%and71%. Square two-dimensional nozzle flow measurement dish was designed. And nozzle flow distribution measurement of TEEJET AITXA nozzle of type8002show that when the nozzle height is0.20m, spray nozzle effective width is about0.24m, and the flow distribution is even with a "double hump" shape. Air-blast spraying nozzle sedimentary characteristics test bench was improved. Spray nozzle droplets sedimentary characteristics experiments show that the smaller the wind speed, the more droplets sedimentary are affected by gravity. Conversely, they are affected by gravity less, and are concentrated in origin area. When the wind speed is more than12m/s and spraying distance is0.80m, droplets sedimentary are concentrated and hardly affected by gravity.