基于变前视距离的四轮同步转向农机改进纯跟踪控制

Improved Pure Tracking Control of Four-wheel Synchronous Steering Agricultural Machinery Based on Variable Forward Looking Distance

路径跟踪控制是提高自主导航系统控制精度的关键。针对在复杂农田作业环境下转弯时纯跟踪算法跟踪精度不高的问题,本文提出了一种基于改进纯追踪模型的四轮同步转向农机路径跟踪控制算法。建立了基于四轮同步转向农机的运动学模型和纯跟踪模型,在此基础上考虑航向误差得到改进纯跟踪模型,进行RTK定位坐标修正,根据量化误差的评价函数搜索前视区域最优目标点,得到最优前视距离。本文算法能实时确定四轮同步转向农机改进纯跟踪模型中的前视距离,使航向误差和横向误差最小化,实现目标点的自适应优化。仿真结果表明,本文方法转弯时平均绝对横向误差减至0.035 m,平均绝对航向误差减至0.212°;水田实验结果表明,当四轮同步转向农机作业速度为3.6 km/h时,四轮转向农机轨迹跟踪平均绝对横向误差减至0.109 m,平均绝对航向误差减至2.799°,转弯跟踪精度显著提高。

The autonomous navigation operation of agricultural machinery has become an inevitable trend in domestic and international development,and path tracking control is the key to improving the control accuracy of autonomous navigation systems.In response to the problem of low tracking accuracy of conventional pure tracking algorithms when turning in complex agricultural environments,an novel path tracking control algorithm for the four-wheel synchronous turning agricultural machinery was proposed based on the improved pure tracking model.A kinematic model and a pure tracking model based on four-wheel synchronous steering agricultural machinery were established.On this basis,an improved pure tracking model was obtained by considering heading error.RTK positioning coordinates were modified,and the optimal forward looking distance was derived from the optimal target points in the forward-looking area according to the evaluation function of the quantitative error.The proposed algorithm can obtain the appropriate forward looking distance in real-time for the improved pure tracking model of four-wheel synchronous steering agricultural machinery,which minimized heading and lateral errors and achieved adaptive optimization of target point.The simulation results showed that the average absolute lateral error of the method during turning was reduced to 0.035m,and the average absolute heading error was reduced to 0.212°.The paddy field experiment showed that when the operating speed of the four-wheel synchronous steering agricultural machine was 3.6km/h,the average absolute lateral error of the four-wheel steering agricultural machine trajectory tracking was reduced to 0.109m,the average absolute heading error was reduced to 2.799°,and the turning tracking accuracy was significantly improved.