微型无人机低空变量喷药系统设计与雾滴沉积规律研究

Design of Variable Spraying System and Influencing Factors on Droplets Deposition of Small UAV

针对我国施药机械和农药使用技术严重落后带来的农药用量大、资源有效利用率低、农作物产量和品质下降等问题,设计了微型无人机脉宽调制型变量喷药系统,并利用风洞的可控多风速环境,通过荧光粉测试方法对悬停无人机变量喷药的雾滴沉积规律进行了试验研究。变量喷药系统由地面测控单元和机载喷施系统两部分组成,基于Lab Windows/CVI的地面测控软件,采用频率为10 Hz、占空比可调的脉冲信号经无线数传模块远程控制机载喷施系统;机载喷施系统以ARM Cortex-M3系列的STM32F103VC微处理器为核心,接收地面控制信号实时调节电动隔膜泵电动机转速,以改变系统喷雾压力和喷药量,实现变量喷雾调节。悬停风洞试验中,选择了PWM占空比、喷孔直径、电动离心喷头转速等变量,对不同距离和风速条件下雾滴沉积效果进行了试验研究。试验结果表明,风速是影响雾滴沉积效果的最显著因素,雾滴沉积以抛物线形式分布在采集区域,沉积高峰区随风速增加不仅远离喷头,且飘移沉积量逐渐减少;雾滴粒径在风速小于3 m/s时对沉积效果影响不显著,当风速大于3 m/s时,不同粒径的雾滴均发生飘移,飘移沉积量明显减少且沉积范围向远离喷头运动;粒径101.74μm的雾滴更易发生飘移,沉积高峰区集中在距离喷头4 m以外,且飘移沉积量明显低于粒径164.00μm与228.16μm的雾滴。

A pulse width modulation（ PWM） variable spraying system based on miniature unmanned aerial vehicle was developed,and based on controllable multi- speed environment,a droplet deposition test through droplets concentration method was studied for the PWM spraying system when the UAV was hovering. The system is consisted of airborne spraying device and ground measurement and control unit.The airborne spraying device with the MCU of STM32F103 VC was remotely controlled by the ground measurement and control unit which was developed by Lab Windows / CVI through wireless data transmission module. Frequency of 10 Hz square wave and adjustable duty ratio were evaluated to control micro electric diaphragm pump,and then pressure and flow rate of the system were changed. The experiments were carried on under the condition of different distance and wind speed to get the relationship among deposition volume,duty ratio,nozzle type,and the rotate speed of centrifugal nozzle.The results showed that wind speed was the most significant factor influencing the droplet deposition.Deposition volume was distributed in a parabolic type in the collection area,gradually decreased and the deposition peak was far away from the nozzle with increasing of wind speed. Droplet diameter was not very important to deposition when wind speed was smaller than 3 m / s. When the wind speed was greater or equal to 3 m / s,the droplet was drifted of different diameters,and the deposition volume reduced significantly and moved away from the nozzle. Small droplet size（ 101. 74 μm） was much easier to be drifted,and the peak concentration was 4 m far from the nozzle. Also the deposition volume of small droplet size was much lower than droplet size of 164. 00 μm and 228. 16 μm. The optimization of spraying parameters and a theoretical support to improve the quality of aviation operations were provided by the results.