NF-752型履带式拖拉机自动驾驶系统

为了提高自动驾驶系统对车身纵向速度和滑移工况等影响因素的自适应能力，提出了一种基于航向预估模型的路径跟踪控制算法。首先对NF-752型履带式拖拉机进行适应性改造，将其手动转向机构和无级变速机构改造为大扭矩舵机控制，通过绝对值编码器测量两侧履带转速，利用RTK-GNSS定位系统测量车辆地理位置和车身速度，结合车载计算机和底层控制器搭建了自动驾驶系统试验平台。然后以车身速度和两侧履带速度为状态变量，考虑履带滑移率建立了航向预估控制模型，进而提出了一种基于航向预估模型的路径跟踪控制方法。最后在沥青路面分别以低速（1 km/h）、中速（5 km/h）和高速（9 km/h）进行了直线路径跟踪试验，结果显示，在不同作业速度条件下，路径跟踪误差无明显差异，最大跟踪误差为-2.00 cm，标准差为0.93 cm。进行了田间曲线路径跟踪试验，结果显示，当拖拉机以6 km/h速度跟踪曲线路径时，跟踪误差优于10 cm，在滑移区域无明显误差增大现象。试验表明，提出的航向预估控制方法对作业速度有较好的适应性，一定程度上克服了滑移现象对控制精度的影响，可满足履带拖拉机耕整地作业精度要求。 

Automatic Driving System for NF-752 Tracked Tractor

In order to improve adaptability of autopilot system to influential factors such as longitudinal speed of agricultural vehicle and slip condition，a heading estimation algorithm based on slip rate estimation was proposed.Firstly，NF-752 crawler tractor was adaptively modified to build a tractor autopilot system test platform，its manual steering mechanism and stepless speed change mechanism were transformed into electrical signal controled by high torque steering engines，vehicle location and body speed were measured by RTK-GNSS positioning system.Secondly，based on vehicle speed and crawler speed on both sides as state variables，course control model was established considering crawler slip rate，and then a path tracking control method was proposed based on this model.Finally，straight path tracking tests were carried out on asphalt pavement at low speed（1 km/h），medium speed（5 km/h）and high speed（9 km/h），results showed that there was no significant difference in path tracking error under different operating speed conditions，and maximum path tracking error was -2.00 cm，standard deviation was 0.93cm.Curve path tracking experiments were carried out in experimental field，and results showed that when tractor tracked curve path at 6 km / h，tracking error was better than 10 cm，and there was no obvious error increase in slip area.Experimental results showed that proposed method had good adaptability to operation speed，and overcome influence of slip phenomenon on control precision.