脉宽调制间歇喷雾变量喷施系统的静态雾量分布特性

Static spray deposition distribution characteristics of PWM-based intermittently spraying system

由于脉宽调制(PWM)间歇喷雾式变量喷施系统的间歇喷雾特性,其雾量分布均匀性较难控制,为此该文采用隔膜泵、比例溢流阀、高速开关电磁阀、TR80-05型空心圆锥雾喷头和工控机测控系统等构建了一套PWM间歇喷雾式变量喷施试验系统,并对其静态雾量分布特性进行了试验研究。在不同喷雾压力、不同PWM信号频率和占空比下,采用矩阵式雾量收集装置对PWM喷头的静态雾量分布进行了测试,并采用非线性回归分析法确立了喷雾压力0.3MPa、PWM信号频率2Hz、不同PWM信号占空比下的集雾单元尺度上的静态雾量分布模型。结果表明:TR80-05型空心圆锥雾喷头的静态雾量分布模型呈中心对称的圆环状,且近似符合二维双正态分布;随喷雾压力的增大,雾量沉积量增加,且雾量分布圆环区域半径增大;PWM信号占空比与雾量沉积量近似呈正比关系,而对雾量分布圆环区域半径的影响较小;PWM信号频率对静态雾量分布影响很小。

Owing to its intermittently spraying characteristics, spray deposition distribution uniformity of PWM-based variable rate application system is hard to control. A PWM-based variable rate application testing system was constructed by integration of a modified commercial boom sprayer and an IPC-based measurement and control system to study its static deposition distribution characteristics. The sprayer consisted of a fluid tank, a filter, a diaphragm pump, a proportional relief valve, 12 high speed on-off solenoid valves, 12 TR80-05 hollow-cone nozzles and various pipelines, mounted on a tractor, and was driven by the tractor via its power take-off shaft. The IPC-based measurement and control system was composed of a pressure sensor, 4 flow sensors, a signal conditioning module, an IPC, an analog input data acquisition card、a PWM signal output card、an analog output card, and 2 driving modules. Real-time monitoring of subgroup flow and boom pressure, feedback stable control of average boom pressure, setting of the average boom pressure, and setting of frequency and duty cycle of the PWM signal were performed by the measurement and control software which was developed with Labview. Droplets were collected with a matrix-styled droplet collection device, it had a horizontal collection dimention of 1000 mm×1000 mm and was divided evenly into 20×20 grids. Putting a paper cup in each grid, weighting the cups before and after each spraying test, droplet deposition of each grid could be deduced, and two-dimentional deposition distribution was obtained. Static deposition distributions of the PWM controlled nozzle were tested under various spray conditions of different spray pressures, different frequencies and duty cycles of PWM signal with the tractor holding still and the tested nozzle 0.5 m distance above the droplet collection area. And nonlinear regression analyses were performed on static deposition distribution specimens acquired under spray conditions of 0.3MPa spray pressures, 2Hz PWM signal frequency and different PWM signal duty cycles to construct their static deposition distribution models on dimension of droplet collection grid unit. Test and analysis results show that static deposition distribution models of the TR80-05 hollow-cone nozzles have a centrosymmetric shape of circular ring and accords with the two-dimensional dual normal distribution, droplet deposition and radius of the deposition circular ring increase with the increasing of spray pressure, droplet deposition is approximately proportional to the duty cycle of PWM signal, the duty cycle of PWM signal has less effect on radius of the deposition circular ring, and the frequency of PWM signal has less effect on the static deposition distribution.