Spray Deposition Characteristics Of Tilt Sprayer Boom And On-line Detection And Control Method Of The Boom Height

Control measures for crop diseases and insect pests mainly rely on chemical pesticides.Boom sprayer is the most widely used machine for pesticide application in the field,but wide-boom will have a large tilt rotation during field spraying application,resulting in uneven droplets distribution and reducing the effect of pesticides,even threatening the safe production of crops.Due to the lack of research on the droplets deposition characteristics of the tilted sprayer boom,the theoretical basis for the adjustment of tilted sprayer boom cannot be provided,and it is difficult to carry out the design research on the boom height control system,which has not met the requirements of the large boom sprayer for modern agricultural production.The on-line detection and adjustment technology of boom height is an effective means to maintain the height of the boom.In this paper,the wide-boom is taken as the research object,with the aim of improving the boom height stability during field application,the droplets distribution characteristics of tilt boom,the online detection method of boom height,the characteristics of boom height change in field and the boom height adjustment method are carried out.The main research content includes 5 parts:(1)Spray characteristics simulation and experiment of flat-fan nozzle based on CFD discrete phase model.Based on the CFD discrete phase model,four liquid sheet structures were constructed to simulate the spray characteristics of the flat-fan nozzle.The simulation results showed that the length of the liquid sheet had a greater influence on the droplet size of the flat-fan nozzle in simulated spray.The liquid sheet length needed to be set according to the spray pressure.Compared with the other three structures,the relative error of droplets R-R distribution diameter(d_e)from sec-model liquid sheet structure was the smallest,and the error value was less than 12%.The flat-fan nozzle sec-model liquid film structure parameter equations were constructed,and the verification test showed that the simulation d_e using the liquid sheet parameters calculated by the sec-model was good agreement with the measurement results.(2)Droplets distribution characteristics CFD simulation and verification of the tilt sprayer boom.Based on the sec-model,A Fluent software was used to construct the boom droplets deposition distribution model,and the droplets distribution of tilt sprayer boom was researched with CFD.And a mobile droplets collection platform was designed to obtain the droplets distribution of tilt boom using a step-by-step collection method,which was used to verify the simulation results.The test results showed that the coefficient of variation(CV)of simulation and spray deposition tests increased with the boom tilt angle,and the maximum CV of simulation and test were as high as 41.43%and 38.34%,respectively.Within the tilt angle of 0-3°,the CV of simulation and test were 11.85%,11.85%,13.03%and 13.32%and 12.81%,13.58%,15.66%and 16.11%,respectively.The simulated and experimental values were in agreement,indicating that the model could predict the droplets distribution characteristics of tilt boom.The droplets deposition tests showed that the tilt boom had a greater influence on the droplets distribution of the boom in a lower spray height.When the boom in a large tilt angle,there was excessive droplets deposition area and missed arer.The uniformity of the droplets distribution was reduced under tilt boom,and the CV was greater than 15.66%with the tilt angle more than 2°,which indicated the boom in this pattern could not be used for field spraying,and the boom height needed to be adjusted.(3)Research on boom height detection method based on ultrasonic sensor.On the basis of a self-designed boom height detection test platform with an ultrasonic sensor,the detection performance of the sensor on regular step and field ground was studied through experiments,and wheat canopy detection tests were carried out.The test results showed that ultrasonic sensor could effectively follow the height changes of regular steps and field ground,and there were a few glitch signals when detecting regular steps and field ground with maximum signal glitch rate of 0.22%and 2.15%,respectively.The speed had an effect on the detection accuracy,and the detection accuracy decreased with increasing the speed.The wheat canopy detection tests showed that the wheat canopy detection data from ultrasonic sensor was discrete,and the detection data value of canopy and non-canopy needed to be separated by the K-means clustering algorithm.After clustering process the detection data,it was found that the ultrasonic sensor could effectively detect the wheat canopy.The detection result was larger than the actual distance and the detection deviation became larger as the wheat density decreased.In order to obtain a more accurate canopy distance,the detection result correction values of D1,D2,D3,D4 and D5 wheat canopy were-0.11,-0.105,-0.135,-0.155,and-0.195 m,respectively.(4)Research on the change characteristics of boom height in field.A boom height detection system was designed based on ultrasonic sensors to monitor the height variation.A GPS positioning receiver was used to obtain the sprayer position in real time.All the detection data were conveyed based on CAN bus.A 2 ha vacant field test and a 13.44 ha wheat stubble field test were carried out using the system.Distribution maps of the boom height variation at different speeds were drawn with Arc Map software.Soil slope test showed that the speed would affect the ultrasonic sensor response to the height variation;compared with the speeds of 5 and 7 km/h,the detection performance of 9 km/h was reduced,and the average detection error was increased from 2.5 and 5.5 cm to 15.1 cm.Field tests in vacant field and wheat stubble field showed that ultrasonic sensors could monitor the boom height variation successfully.At the speeds of 5,7 and 9 km/h,the boom height variation mainly occurred on the left and right booms,while the middle boom changed little.As the speed increased,the height variation of the left and right booms increased.The maximum swing amplitudes of boom ends were 105.6?118.4 and 124.4 cm respectively,and the maximum tilt angles were 3.3,3.5 and 3.6°respectively in the vacant field.The maximum swing amplitudes of boom ends were 98.6,103.1 and 116.5 cm respectively,and the maximum tilt angles were 2.6,2.7 and 2.8°respectively in the wheat stubble field.During the spraying process in wheat stubble field,as the wheat stubble height increased,the swinging amplitudes of left and right booms increased.The average swinging value was 32.6 cm with a maximum value of 102.3 cm in normal operation,and the average swinging value was 57.8 cm with a maximum value of 104.9 cm in turning operation.There was a risk of tilt boom colliding with crop canopy or ground.In order to ensure the droplets uniformity and avoid damage the boom and crops,the boom height needed be adjusted,especially in the left and right booms height.(5)Design and test of automatic control system for boom height.An automatic height adjustment system for the boom was designed based on the ultrasonic sensors.The height of the three-section boom would be adjusted through the hydraulic system.Ground tests were carried out to compare the spray deposition characteristics in unadjusted pattern and adjusted pattern.The results showed that the impact of the boom in unadjusted pattern on the spray height was significant when the sprayer passed a step track,especially in the left and right booms,and similar results were also obtained in the droplet distribution.In adjusted pattern,there was a relatively small effect on the spray height and droplet distribution when the boom passed through the step track.The CV was up to 30.06%when the boom passed through the step track in unadjusted pattern,while in adjusted pattern it was less than 12.35%.The automatic control system of boom height could keep the boom at an appropriate spray height,which helped to improve the spray deposition uniformity of the boom and the use efficiency of pesticides,and could greatly reduce the equipment and crop damage caused by the boom hitting the ground and crops.