基于PWM的电控精量喷雾控制系统设计与试验

Design and experiment of electronically controlled precision spray control system based on PWM

针对现有变量喷雾系统精准化程度低、农药有效利用率低等问题,设计一种基于PWM的电控精量喷雾控制系统。该系统以PIC18F258单片机为核心,主要由上位机、喷雾控制器、电子开关、电控喷嘴体组成。采用HMI串口屏作为上位机,接收用户设置的喷药量,通过CAN总线通讯实时发送到喷雾控制器;喷雾控制器根据接收的施药量计算出对应喷头的PWM占空比,实时调节各个喷头单位时间的通断时间,从而实现喷头的独立控制。为验证系统控制的精确性,在脉冲频率为10 Hz,系统压力分别为0.3 MPa、0.4 MPa、0.5 MPa时,测量喷雾系统在单个周期内的喷雾时间、系统响应时间以及不同占空比下的喷头流量。试验结果表明:在系统压力分别为0.3 MPa、0.4 MPa、0.5 MPa下,喷头流量与PWM占空比之间均为线性关系,线性拟合度均大于0.95。电控喷嘴体通断时间误差最大值分别是2.5 ms、2.98 ms、2.9 ms,相对误差最大值分别是6.6%、6.6%、6.8%,RMS误差分别为2.37 ms、2.54 ms、2.27 ms,喷雾系统最大响应时间分别为0.179 s、0.176 s、0.167 s。

Aiming to address the problems of low precision of variable spray systems and low effective utilization rate of pesticides,this research designed an electronically controlled precision spray control system based on PWM.The system takes PIC18F258 single-chip microcomputer as the core,which is mainly composed of an upper computer,spray controller,electronic switch,and electronically controlled nozzle body.The system also has an HMI serial port screen that is used as the host computer to receive the spray amount set by the user and send it to the spray controller in real time through CAN bus communication.The spray controller then calculates the PWM duty cycle of the corresponding nozzle according to the received application amount,and adjusts the on-off time of each nozzle in real time to realize the independent control of the nozzle.In order to verify the accuracy of the system control,when the pulse frequency is 10 Hz and the system pressure is 0.3 MPa,0.4 MPa,and 0.5 MPa,respectively,the spray time,system response time,and nozzle flow under different duty ratios of the spray system in a single cycle were measured.The test results showed that under the system pressure of 0.3 MPa,0.4 MPa,and 0.5 MPa,the relationship between nozzle flow and PWM duty cycle was linear,and the linear fitting degree was greater than 0.95.The maximum errors of the on-off time of the electronically controlled nozzle body were 2.5 ms,2.98 ms,and 2.9 ms,the maximum relative errors were 6.6%,6.6%,and 6.8%,the RMS errors were 2.37 ms,2.54 ms,and 2.27 ms,and the maximum response time of the spray system was 0.179 s,0.176 s,and 0.167 s,respectively.