摘要
为克服机械被动仿形中弹簧形变量变化导致开沟深度不一致的问题,该文采用主动仿形方法设计开沟深度定压电液仿形控制系统,该系统基于PLC控制单元,以压力传感器检测的开沟器入土压力与设定值的偏差作为控制信号,控制电液比例减压阀输出压力,保证开沟器入土压力恒定,主要由机械系统、液压系统、控制系统组成。基于理想土壤条件下一定开沟深度对应的仿形压力输出要求,确定了系统液压回路结构、液压元件型号与参数以及控制元件类型与参数、硬件连接方式等,并开发了相应的软件程序。分别建立电液比例减压阀、液压缸、平行四杆机构等系统组成环节的传递函数,得到系统闭环传递函数,利用MATLAB对系统进行稳定性判别与单位阶跃响应分析。仿真结果表明,控制系统运行稳定,超调量为5.02%,响应时间为0.25 s,稳态误差为0.79%。搭建液压试验台,采用液压缸模拟地表起伏状况进行仿形系统试验,结果表明,在20~200 N的开沟力、10~80 mm的开沟深度时,系统的平均响应时间为0.27~0.36 s,最大响应时间为0.4 s;平均稳态误差为1.4~1.8 N,最大稳态误差为2.7 N,标准偏差为0.78%~6.94%。试验值与仿真结果相比,平均响应时间高出4%~44%,最小标准偏差与稳态误差相差0.01%,验证了系统模型的可靠性与准确性。本文设计的控制系统降低了基于压力传感器的电液仿形控制系统的响应时间与稳态误差,可为电液仿形控制系统参数设定与理论分析提供借鉴。
The consistency of sowing depth is one of the most important indicators for the seeder. It will not only affect the germination rate of seeds, but also cause inconsistency in plant height which will reduce the quality of the following mechanized such as plant protection and harvesting. Spring profiling is a passive profiling method that has been widely used in ditching depth control at present, but the ditching depth cannot be consistent, because the pressure on the furrow opener is changed with the spring deformation. Using an active profiling method, a consistent pressure control system for the furrow opener was designed, which was composed of the parallel four-bar mechanical system, the hydraulic system and electronic control system. Based on the programmable logic controller, the system controlled the output pressure of the electro-hydraulic proportional reducing valve according to the deviation between the setting pressure and the value detected by the pressure sensor on the furrow opener, making the output pressure of the cylinder and the vertical earth pressure of opener consistent. The parameters of the control system was determined, including the hydraulic circuit of the system, parameters of hydraulic components, types and parameters of control components, hardware connection and software program. To judge the stability and analysis the unit response of the system by using MATLAB, the closed-loop transfer functions of the system was established based on building the transfer function of each link, such as the electro-hydraulic proportional reducing valve, hydraulic cylinder and parallel four-bar mechanism and so on. The simulation results showed that the system was stable, and the static overshoot was 5.02%, the response time was 0.25 s, and the steady-state error was 0.79%. According to the simulation results, the system was debugged and tested using another hydraulic cylinder to simulate the grand surface fluctuation. When the vertical earth pressure of the opener was set at 20 to 200 N, the profiling depth was set at 10 to 80 mm, the experiment results showed that the average response time of the system was about 0.27-0.36 s and the steady-state error was 1.4-1.8 N with the maximum 2.7 N, and the average standard deviation was 0.78%-6.94%, the output pressure was consistent. It also concluded that the response time decreased with the increasing of the profiling depth and the earth pressure, while the steady-state error were not effect by the above two factors, and the average standard deviation decreased with the increase of the earth pressure, so the greater earth pressure was beneficial for higher accuracy of the system. Compared with the simulated results which the response time was 0.25 s and the steady error was 0.79%, the average response time of the experiment was 4%-44% higher and difference between the minimum standard deviation of the experiment and the steady error was 0.01%, verifying the reliability and accuracy of the system model built. The research reduced the response time and the steady error of the electro-hydraulic profiling system based on the pressure sensor, providing the reference for the parameter setting and theoretical analysis of electro-hydraulic profiling control system.
作者
梁方
雷淇奥
郑思远
王鹏
郭洲
刘伟
Liang Fang;Lei Qi’ao;Zheng Siyuan;Wang Peng;Guo Zhou;Liu Wei(College of Engineering,Huazhong Agricultural University,Wuhan 430070,China;Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River,Ministry of Agriculture and Rural Affairs,Wuhan 430070,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2019年第21期1-8,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家重点研发计划项目(2017YFD0700702)
湖北省自然科学基金项目(2018CFB343)
关键词
农业机械
设计
试验
开沟深度
仿形
压力控制
响应时间
稳态误差
agricultural machinery
design
experiments
ditching depth
profiling
pressure control
response time
steady-state error
