基于DGPS与双闭环控制的拖拉机自动导航系统

Automatic Navigation System of Tractor Based on DGPS and Double Closed-loop Steering Control

以东方红X-804型拖拉机为平台,设计了一种基于RTK-DGPS定位和双闭环转向控制相结合的自动导航系统,研究提高农业机械导航控制精度的方法。阐述了导航系统整体设计方案,以RTK-DGPS和AHRS500GA分别提供位置信息和辅助修正信息实现准确定位,以电控液压转向系统实现转向控制。分析了整体控制的策略,建立了路径跟踪的传递函数模型,阐述了双闭环转向控制算法的建立过程,以及控制器的硬件实现。试验结果表明:GPS定位数据经过校正后,平均偏差降低至0.031 m;双闭环控制算法提高了自动转向系统性能,稳态时方波信号以及正弦波信号的跟踪误差平均值为0.40°;在拖拉机田间作业跟踪过程中,路径跟踪误差平均值不超过0.019 m,转向轮偏角跟踪误差平均值为0.43°,标准差不超过0.041 m。

An agricultural automatic navigation system was designed on Dongfanghong X-804 tractor to improve the navigation control of agricultural machinery by using RTK-DGPS and double closed-loop steering control. The make-up of the whole navigation system and working principle were presented,among which their main features were： RTK-DGPS could offer positioning data,including heading,roll and pitch parameters, which were acquired from AHRS500 GA, and the electro-hydraulic steering controller was developed for automatic steering control. Then,the system control strategy was analyzed and the control transfer function model was developed for trajectory tracking,with a double closed-loop control algorithm for steering system designed according to characteristic of the system nonlinear. The implementation description on an ARM9E-based embedded control system was provided in terms of electronics hardware design. Tests were conducted to examine the navigation system,including a straight line driving test on uneven road,which was to verify the effectiveness of the correction model. The test results showed that the proposed positioning and orientation evaluation algorithm could eliminate the effects of uneven field condition on GPS positioning and the average error of GPS positioning was reduced to 0. 43°. Then a test of steering control system was carried out to verify the performance of double closed-loop control algorithm. Test results showed that the steering control system solved the control overshoot well and the average error was 0. 40°. Finally, the field test results showed that the performance of automatic navigation system was improved,with average route tacking error was less than0. 019 m,average steering angle tracking error was 0. 43° and standard deviation was less than 0. 041 m.The field test results indicated that the proposed positioning evaluation algorithm and double closed-loop steering control algorithm on uneven field were appropriated to Dongfanghong X-804 tractor.