Research On Tree On-line Detection Method And Targeted Variable-rate Spraying Techniques Based On Laser-scanning Sensor

Chemical control is the main method for pest control in plant protection.Excessive waste and large residues of pesticide will be caused by the continuous spraying method of traditional sprayer,which causes serious pollution to the environment.Precision pesticide application in orchard is one of the important way to improve pesticide application efficiency and reduce pesticide residues.To avoid overspraying while ensuring the pest control effect,targeted variable-rate spraying techniques applied in orchard were studied based on the tree canopy online detection.The main contents and results of the research are as follows:1.A tree canopy on-line detection method was proposed based on a laser-scanning sensor,which included a tree canopy grid partition method and a gridding volumes model.The influence on the detecting accuracy caused by detecting angle error was analyzed and on-line detection experiments of regular objects and different trees were conducted to evaluate the detecting accuracy.The experiments of regular objects showed that the maximum relative errors of grid volumes of the cuboid,triangular prism and cylinder objects were 3.3%,7.9%,and 9.4%,respectively;the total volumes detected under different detecting speeds were very close,with maximum relative error less than 5%,which illustrated that the gridding volumes model was able to obtain the volume of each section and the total volume of the regular object precisely at different speeds.The 3D reconstruction model of two cherry-apple trees with different canopy density was able to reflect the canopy characteristic details;the maximum variation coefficients of total volumes for each kind of the tree were 0.058 and 0.017,respectively.The total volumes of a conifer tree and an apple tree under different detecting speed of 1.5,3.0 and 4.5km/h showed no big difference respectively.However,the maximum variances of the total volumes detected at different grid sizes increased gradually.It illustrated that the detecting accuracy would decrease when the grid sizes were getting bigger.The variation coefficients of the total volumes were 0.078 and 0.041 respectively,which indicated that the detecting system could obtain tree canopy volumes with high repetitive detection accuracy.2.A method of calculating spray data which were consisted of duty cycles of Pulse Width Modulation(PWM)was proposed based on a spray volume model.The flow calibration tests of sprayer nozzles were conducted in the constant pressure spray system,which was designed based on incremental PID control,and the spray system of sprayer respectively.The results illustrated that the nozzle flow rate had a good linear correlation with the PWM duty cycle between 10%and 60%,and reached the maximum flow between 60%and 90%.The nozzle flow models were established in group to ensure the accuracy of the spray volume because the adjustment range of the nozzle flow rate decreased with the height of the nozzle and the pipe length between the solenoid valve and the nozzle increasing.The optimized installation scheme of the solenoid valves and the nozzles was proposed by analyzing the pressure loss along the pipe,which was minimizing the pipe length to obtain larger flow rate adjustment range.3.A variable-rate spray control system and an air-assisted sprayer prototype integrated with a laser-scanning system were developed to realize targeted variable-rate spraying.Meanwhile,a spray delay control method was proposed to eliminate the influence of sprayer travel speed on the targeted spray.The results of the targeted spray experiment showed that the distance error between the detection positions and the corresponding spray positions would be getting bigger with the increasing of gird width,while the distance errors were in the same range at speeds of 1.0,1.5 and 2.0 m/s respectively after the gird width was determined,which indicated that the accuracy of the spray delay control method wasn't influenced by the travel speed.When the grid width was 210mm,the distance error was reduced to a smaller range between-35mm and 35mm by adding a spray delay distance compensation,which indicated that the spray delay control method was practical to realize the targeted spray with high accuracy.4.The effects of different grid sizes and travel speeds on the spray performance were evaluated by quantifying spray coverage uniformity and deposition density inside tree canopies.The results showed that spray coverage uniformity declined with increasing grid width from 0.14 to 0.28 m although the mean spray coverage on each target location showed no significant differences.Additionally,there were no significant variations in mean spray coverage at speeds of 1.0,1.2 and 1.4 m/s for a tested tree of 1.6 m width and at any experimental speeds for a tested tree of 1.3 m width;However,it was declined at any experimental speeds for a tested tree of 2.4 m width,which indicated that the variable-rate sprayer could provide good spray coverage uniformity under various travel speeds with a canopy size limitation.Compared with the same sprayer without the variable-rate spray function,the intelligent sprayer prototype realized effective toward-target spraying and avoided overspraying while providing sufficient pesticide to achieve the pest control effect.