精密播种机下压力和播深CAN总线监控与评价系统研究

为实现精密播种作业中播种下压力和播深的实时监控和质量评价,设计了一种多行播种机下压力和播深CAN总线监控与评价系统。系统采用基于角度和轴销传感器的播深和下压力测量装置,优化设计了液压驱动和分区控制的气压驱动装置,开发了基于CoDeSys(Controlled development system)编程环境的智能终端交互界面和ECU(Electronic control unit)控制程序,实现了基于CAN总线通信的作业参数监测控制和质量评价。通过搭建的室内试验台完成了播深和下压力静态建模试验,建立了适应不同设定播深的下压力测量模型。分区控制系统响应测试试验表明,在调节范围(0.2~0.6 MPa)内,系统超调量低于5.97%;响应时间与控制行数和设定气压正相关;在设定气压(0.1~0.6 MPa)范围内,6行播种机调节时间不超过2.35 s。为测试系统工作性能,在25、50、75 mm 3种设定播深下,对左区控制(600 N)、右区控制(300 N)、机械调节和自重调节4种控制方式进行了田间性能试验。土壤压实和播种下压力控制效果试验表明,主动分区控制方式可实现更为稳定的土壤紧实度,且在浅旋地块环境下,右区控制方式可达到最优的下压力稳定性,其控制合格率不小于95.78%;播深控制效果试验表明,随着设定播深的增大,播深质量显著降低,在设定播深25~75 mm范围内,左区控制、右区控制、机械调节和自重调节对应的最小播深合格率分别为91.92%、92.53%、70.44%和58.72%,对应的最大标准差分别为2.22、3.11、3.69、7.70 mm,对应的最大变异系数分别为3.52%、4.40%、4.96%和14.01%。相比机械调节和自重调节,分区控制系统提高了单体下压力和播深稳定性。

Development of CAN-based Downforce and Sowing Depth Monitoring and Evaluation System for Precision Planter

The adequate seeding downforce and consistent sowing depth are beneficial to improve the seedling quality in the precision planting operation.To avoid the problems of undesired soil compaction and uneven germination caused by the change of soil conditions,and realize the intelligent monitoring and evaluation of the sowing quality,the design of a downforce and sowing depth monitoring and evaluation system was presented for the multi row-crop planter.The system was mainly composed of downforce measurement device,sowing depth measurement device,electronic control unit(ECU)for data acquisition and actuator control,GNSS receiver,intelligent terminal and pneumatic driving device.The downforce and sowing depth measurement devices were applied to measure the downforce acting on the gauge wheels and the sowing depth based on the axle pin sensor and the angle sensor of limit shank respectively.The pneumatic driving device was used to provide the necessary downforce,which mainly included air-spring,gas generator,electric-gas proportional valve and gas tank.In order to quickly replenish the air loss caused by the rapid regulation of downforce and improve the response speed of the system,a section control method for the pneumatic driving device was adopted,and the gas generator with a double cylinder air pump was driven by a hydraulic motor.In addition,a human machine interface(HMI)of the intelligent terminal and the control program of ECU were developed based on controlled development system(CoDeSys)programming environment to realize the real-time monitoring and evaluation of seeding quality through CAN bus communication.To improve the accuracy of measurement,the static modeling tests of sowing depth and downforce were conducted on an indoor test platform and a downforce measurement model integrating sowing depth variable was established.The response characteristic test of the control system showed that the step response overshoot was less than 5.97%,and the adjustment time was positively related to the control row-unit number and the set air pressure in the range of 0.1~0.6 MPa,which was not more than 2.35 s for the six row-units planter.Furthermore,in order to test the performance of the system,field performance experiments were carried out with four control modes(left section control with 600 N target downforce,right section control with 300 N target downforce,mechanical adjustment with helical spring and dead weight adjustment of row-unit)and three setting sowing depths(25 mm,50 mm and 75 mm).The experiment of soil compaction and sowing downforce control showed that the section control method could achieve more stable soil compactness,and the right section control method could achieve the optimal downforce stability in the shallow rotary tillage filed with no less than 95.78%qualified rate.The experiment of sowing depth control effect showed that the quality of sowing depth was decreased significantly with the increase of setting sowing depth.In the depth range of 25~75 mm,the minimum qualified rates of left section control,right section control,mechanical adjustment and dead weight adjustment were 91.92%,92.53%,70.44%and 58.72%,the corresponding maximum standard deviations(SD)were 2.22 mm,3.11 mm,3.69 mm and 7.70 mm,and the corresponding maximum coefficients of variation(CV)were 3.52%,4.40%,4.96%and 14.01%,respectively.The above results showed that the system with section control method could improve the consistency of sowing depth and accuracy of downforce,and had better performance of sowing depth and downforce control than the system with mechanical adjustment and dead weight adjustment methods.