基于靶标叶面积密度参数的变量喷雾控制系统开发与性能试验

Development and Performance Test of Variable Spray Control System Based on Target Leaf Area Density Parameter

变量喷雾技术是提高农药利用率、节省农药用量的重要手段之一。为达到果园施药减量增效的效果,本研究开发了一种变量喷雾控制系统,提出了叶面积密度参数与执行机构脉宽调制(Pulse Width Modu⁃lation,PWM)占空比的计算方法。该系统上位机基于激光LiDAR传感器探测的点云密度表征叶面积密度作为施药参数,并根据喷药处方计算各喷头对应电磁阀的PWM占空比,通过RS485通讯实时发送施药处方到下位机的可编程逻辑控制器(Programmable Logic Controller,PLC),下位机PLC根据接收的PWM占空比控制对应电磁阀的开关频率实现喷头喷雾流量的调节。通过试验测量了施药单元网格尺寸、系统延时时间以及PWM占空比与喷头流量之间的模型参数三部分关键系统参数。结果表明在0.2、0.3和0.4 MPa压力下PWM占空比与喷头流量之间均为线性关系,线性拟合优度均在0.98以上。最后,通过喷雾试验验证变量喷雾样机的有效性,试验结果表明,采样点水敏纸上单位面积(cm^(2))最少雾滴个数为35滴,达到了有效喷雾效果;当靶标冠幅与总冠幅比为39.9%时,变量喷雾模式相比于连续恒定式喷雾省药71.96%,相比于对靶开关式喷雾省药29.72%,达到了减量效果。

Variable spray technology is an important means to improve pesticide utilization rate and save pesticide.Fruit tree is a kind of three-dimensional space,and the densities of branches and leaves in the canopy of fruit trees at different locations are different at the same time.The ideal state of spray is to adjust the amount of spray according to local characteristics,so as to re‐alize the application of the spray on the canopy of fruit trees as required and improve the utilization rate of pesticide.In order to achieve the effect of reducing the dosage and increasing the efficiency of pesticide application,a variable spray control system was developed and the methods for computing leaf area density parameter and pulse width modulation(PWM)'s duty ratio of ac‐tuators were proposed.As the dosage parameter,the leaf area density was derived based on the point cloud density detected by LiDAR sensor on the upper computer.Then PWM's duty ratio was calculated based on the leaf area density and sent to the slave computer-PLC in real time.The communication between upper and slave computer was carried out through RS485 standard.So the spray flow of each nozzle was controlled by the switching frequency of the solenoid valve with PWM's duty ratio signal.Key parameters were obtained by the test including the net size of spray unit,delay time of the system and the function relation‐ship between the PWM's duty ratio and the spray flow of nozzle.The test results showed that there was a linear relationship be‐tween the PWM's duty ratio and the spray flow of nozzle under the pressure of 0.2,0.3 and 0.4 MPa,and the linear goodness of fit were all above 0.98.Finally,the effectiveness of the variable spray system was verified by the spray test.The test results showed that the minimum number of droplets per unit area(cm^(2))on the water-sensitive paper was 35 drops at the sampling point,which was higher than the 25 drops defined by the common method for the spray amplitude of aerosol in the air supply spray.Under 39.9%of the canopy ratio between the target canopy area and the whole area,the variable spraying mode saved 71.96%of the pesticide dosage compared with the continuous spraying mode,and 29.72%compared with the target spraying mode,achieving the dose reduction effect.