基于LiDAR的果园对靶变量喷药控制系统设计与试验

Design and experiment of the orchard target variable spraying control system based on LiDAR

传统果园喷药方式带来的非靶标区域农药沉积和飘移造成了环境污染,同时农药过量喷施导致农药残留。该研究基于前期获得的果树冠层网格化体积计算方法建立单喷头流量脉宽调制(Pulse Width Modulation,PWM)控制模型,根据果园喷药作业需求建立控制器局域网络(Controller Area Network,CAN)总线通讯协议,采用高速摄影方法获得喷头开闭延时补偿距离为96 mm,通过实验室试验确定作业速度1 m/s下的最佳网格宽度为210 mm,融合对靶喷药控制方法研发果园激光对靶变量喷药控制系统,并将该系统搭载在果园喷药机上集成研制果园对靶变量喷药机样机。实验室试验表明,喷头开启滞后距离为19 mm,喷头关闭滞后距离为41 mm。果园试验表明,喷头开启滞后距离为122 mm,喷头关闭滞后距离为185 mm;雾滴沉积密度大于20滴/cm^(2)下,对靶变量喷药的雾滴覆盖率低于30%;在设定试验区域内,连续和对靶变量喷药的农药用量分别为4.53和1.71 L,对靶变量喷药节约药量62.25%。该系统可根据果树冠层位置和冠层体积变化实现对靶变量喷药。本研究将推动果园精准喷药技术的快速发展和应用。

Extensive pesticide application can lead to the residues of harmful chemicals,such as highly toxic pesticides and heavy metals in agricultural products.The traditional air-assisted spraying has posed a great risk to human health in environmental ecosystems,particularly for the pesticide deposition and drift of off-target areas.Orchard target-oriented spraying technologies have been used to reduce the deposition and drift caused by off-target spraying,in order to control the environmental pollution within an acceptable range.In this study,a flow Pulse Width Modulation(PWM)model in a single nozzle was established for an orchard tower air-assisted sprayer using the grid volume calculation of the fruit tree canopy.The sprayer was equipped with 10 nozzles on each side.A Light Detection and Ranging(LiDAR)was selected to divide the fruit tree canopy into 10 grids in the vertical direction,where the nozzles had corresponded to the grids one by one.The spray volume was adjusted to control the flow of a single nozzle in different areas of the fruit tree canopy.The adjustment range of the optimal PWM duty cycle was 0-60%.The stability time of pressure PID control in the spray system was less than 3 s,and the pressure control deviation was less than 0.15 MPa.The opening and closing time of the nozzles were obtained through high-speed photography,and the delay compensation distance was determined to be 96 mm at a speed of 1 m/s.A Controller Area Network(CAN)bus communication protocol was then established,according to the spraying requirements in an orchard.A target-oriented variable-rate spraying control system was developed to integrate the target-oriented spraying control with the orchard sprayer.A physical prototype was also prepared in the target-oriented variable-rate sprayer.The laboratory and orchard tests were designed to evaluate the performance of the target-oriented variable-rate spraying control system.A stepped calibration plate was selected to simulate the target in the lab test.The width of each step of the calibration plate was 70 mm.The horizontal distance errors for the ahead or lag of the target-oriented spraying were obtained to compare the starting position of the spraying and the corresponding step position of the calibration plate.The test results showed that:1)The optimal grid width was 210 mm at a speed of 1 m/s.The opening and closing lag distances of the nozzles were 19,and 41 mm,respectively.An evaluation was proposed to verify the target-oriented control accuracy in the orchard test,where a white cloth was used to record the spray range.The horizontal distance errors of the ahead or lag of the target-oriented spraying were obtained to compare the spray width on the white cloth and fruit tree canopy.It was found that the opening and closing lag distances of the nozzles were 122,and 185 mm,respectively.2)A target-oriented variable-rate spraying test was carried out in a 5-year-old peach orchard.The continuous and variable-rate spraying was evaluated to arrange the water-sensitive measurement at the up,middle,down,left,and right positions on the orchard canopy.The spraying volume was recorded in real time.The spray application rate was evaluated to compare the continuous spraying,according to the spraying volume.It was found that the spray coverage of the target-oriented variable-rate spraying was less than 30%under the spray deposit densities greater than 20 deposits/cm^(2),which was much lower than the defined threshold for the overspray.The spray volumes were 4.53 and 1.71 L,respectively,for the constant-rate and target-oriented variable-rate spraying in the test area,indicating 62.25%less spray volume.As such,the target-oriented variable-rate spraying can be widely expected to fully realize the requirements in an orchard,in terms of the canopy position and volume changes of the fruit tree.This finding can also be used to rapidly promote the application of precision spraying technology in orchards.