| At present,chemical control is still the main technical means to control diseases and insect pests in orchard plant protection.Traditional large-capacity continuous spraying,regardless of target and individual differences,has caused waste and residue of pesticides in orchard spraying process,which has further affected fruit quality and caused environmental pollution.It is crucial to solve this problem by studying variable-rate spraying technology in orchards.In order to achieve the goal of reducing pesticide dosage and increasing pesticide efficiency,this paper has studied key technology of orchard variable-rate spraying,which will improve utilization of pesticides and the quality of fruit.The main research contents and significance are as follows:(1)Orchard variable spray test bed was designed,which is mainly composed of variable spray system,air-conveying system and control system.In this paper,relevant design and simulation of key components of orchard variable spray test bed were carried out.In the test bed,PWM wave with a frequency of 12 Hz is used to control the flow rate of single nozzle,and air volume at outlet is changed by means of branch air regulation,so as to realize precise control of air-conveying variable spray.Sensor fusion array is used to improve accuracy of canopy measurement,and it is compared with single sensor array to test by response surface method.Test results show that: when the vehicle speed is 0.3-0.5 m/s,relative error of canopy width detected by ultrasonic sensor array is 14.56-20.41 %,and relative error of canopy width detected by laser sensor array is 9.73-16.85 %.The relative error of canopy width detected by sensor fusion array is only 4.2 ～ 11.24 %.Therefore,compared with accuracy of canopy width detected by the single sensor array,sensor fusion array is at least 33.3% higher than that at same vehicle speed.(2)Study on the calculation method of discrete canopy volume.When vehicle is tilting or not tilting,the canopy width of fruit tree within the range set by vehicle body is discretized.The sensor fusion array is arranged at a certain distance in front of the nozzle to judge void between canopy of fruit tree,and then discrete canopy volume model is obtained.According to the relationship between dosage and volume of air and volume of canopy,the control methods of dosage and air-conveying for canopy of fruit trees were obtained.(3)The distribution test of variable spray deposition with single nozzle was carried out outdoors.Test results show that: At same wind speed,total deposition decreases with decrease of duty ratio,decrease of wind speed and increase of spray distance.When the wind speed at outlet is 0 m/s and spray distance is 0.5 m,variation coefficient is 1.28;when spray distance is1.0m,variation coefficient was 0.72;when spray distance is 1.5 m,variation coefficient is0.49.When outlet wind speed is 8m/s,variation coefficients of corresponding spray distances are 1.28,0.63 and 0.44,respectively.When outlet wind speed is 16m/s,variation coefficients of corresponding spray distances are 1.26,0.60 and 0.35,respectively.(4)The dispersion test of canopy width and the test of canopy deposition were carried out in orchards.Test results show that:1)Variation coefficient of discrete canopy width in the top,middle and bottom canopy of continuous dense orchards was 0.021,0.035 and 0.106;variation coefficient of discrete canopy width in the top,middle and bottom canopy of spindle sparse orchards was 0.064,0.118 and 0.239;and variation coefficient of discrete canopy width in the top,middle and bottom canopy of single plant type sparse orchard was 0.097,0.202 and 0.325.2)Compared with single fusion sensor array,the improved fusion sensor array has better effect,which is shown as follows: The number of fog drops in the top,middle and bottom canopy of continuous dense orchard decreased by 6.95 %,3.85 % and increased by 4.40 %,respectively;deposition decreased by 11.11 %,8.33 % and 3.57 %,respectively.The number of fog droplet deposition in the top,middle and bottom canopy of spindle sparse orchard decreased by 27.08 %,30.37 % and 18.55 %,respectively;deposition decreased by 64.71 %,60.86 % and 40.38 %,respectively.The number of fog droplet deposition in the top,middle and bottom canopy of single plant type sparse orchard decreased by 18.44 %,26.26 % and15.54 %,respectively;deposition amount decreased by 40 %,42.42 % and 41.46 %,respectively. |
