基于DGPS定位与双闭环转向控制的农业自动导航系统

Agricultural automatic navigation system based on DGPS positioning and double closed-loop steering control

以东方红X-804拖拉机为平台,开发了一种基于RTK-DGPS定位和双闭环转向控制相组合的农业自动导航系统。系统主要包括RTK-DGPS接收机、姿态航向参考系统(AHRS)、转向控制器、电控液压转向装置和转向角检测传感器。设计了Kalman滤波器对定位数据进行平滑处理,同时实现航向角的校正。为实现自动转向,在拖拉机原有手动控制系统基础上加上电控比例液压阀,并设计电控单元。然后,推导了转向系统的数学模型,通过Matlab仿真工具箱得到传递函数的参数,设计了双闭环转向控制算法。最后,进行了算法验证试验和田间试验,结果表明,双闭环控制方法较好抑制了稳态时的震荡现象,方波信号的角度跟踪稳态时最大误差0.60°,平均误差0.40°,平均延时为0.20 s;设计的Kalman滤波器有助于提高定位系统的精度,横向跟踪误差不超过0.09 m,转向角度平均跟踪误差为0.43°,延时0.25 s。

An agricultural automatic navigation system based on real time kinematic differential global positioning system（RTK-DGPS） and double closed-loop steering control was developed on Dongfanghong X-804 tractor. The system includes RTK-DGPS receiver, attitude and heading reference system（AHRS）, steering controller, electrohydraulic steering actuator and encoder sensor for steering angle testing. One Kalman filter was designed to smooth the collected GPS positioning data and evaluate the bias error of the heading angle. In order to realize automatic steering, an electro-hydraulic proportional valve was added to the original manually operated steering system and the electronic control unit was designed. Then the mathematical model of steering system was derived, using Matlab System Identification Toolbox to estimate transfer function parameters, and a double closed-loop control algorithm for steering was designed. Finally, experimental results of square signal tracking test and field test are presented, showing that the double closed-loop control solved the control overshoot well and the maximum error is 0.60°, average error 0.40°, average delay 0.20 s. The designed Kalman filter is helpful to improve the accuracy of positioning system and the maximum lateral tracking error is less than 0.09 m, average steering angle tracking error 0.43°, average delay 0.25 s.