高级检索+

基于MPC-Stanley的土壤采样平台路径跟踪方法

Path tracking on soil sampling platform using MPC-Stanley

  • 摘要: 针对目前土壤采样平台自动导航过程中路径跟踪控制效果不佳、跟踪精度低的局限性,该研究提出了一种基于MPC-Stanley的土壤采样平台路径跟踪方法。首先,基于土壤采样平台设计了导航系统;其次,搭建了基于自行车模型的土壤采样平台运动学模型;随后,选用模型预测控制(model predictive control,MPC)作为路径跟踪的控制器,基于Stanley控制器优化了MPC控制器中前轮转角控制量,同时根据导航系统对控制量的实时要求修正了控制量;最后,以土壤采样平台为控制对象,采用惯性测量单元(inertial measurement unit,IMU)与卫星定位模块获取土壤采样平台实时位姿信息,开展土壤采样平台田间路径跟踪试验。以直线路径Tr1与曲线路径Tr2为参考路径,测试了平台行驶速度0.8 m/s的循迹效果,同时测试了平台行驶速度0.8、1.6、2.4和3.2 m/s的路径跟踪误差,并将测试结果与纯跟踪(pure pursuit,PP)控制器、比例积分微分(proportional integral derivative,PID)控制器测试结果进行了比对。试验结果表明,相比于其他2种控制器,MPC-Stanley控制器循迹效果最好,跟踪路径更贴近于目标路径;在直线路径Tr1跟踪过程中,MPC-Stanley控制器平均绝对偏差、最大绝对偏差与标准差的平均值分别为3.1、4.7和1.2 cm,相比于PP控制器分别降低了43.6%、43.4%和14.3%,相比于PID控制器分别降低了20.5%、23.0%和7.7%;在曲线路径Tr2跟踪过程中,MPC-Stanley控制器平均绝对偏差、最大绝对偏差与标准差的平均值分别为3.9、6.6和1.5 cm,相比于PP控制器分别降低了80.2%、79.8%和85.7%,相比于PID控制器分别降低了93.0%、89.8%和90.5%,MPC-Stanley控制器在曲线路径跟踪效果更好,可为土壤采样平台高精度导航提供参考。

     

    Abstract: Path tracking performance and tracking accuracy are often required during the autonomous navigation of the soil sampling platforms. In this study, a path tracking was proposed for the soil sampling platforms using MPC-Stanley. Firstly, a hardware architecture of the navigation system was designed for the soil sampling platform. A control scheme was also formulated for the navigation system. Secondly, a kinematic model was constructed using a bicycle model. Subsequently, the model predictive control (MPC) was selected as the path tracking controller, thus deriving the control processes for both the MPC and Stanley controllers. The Stanley controller was employed to optimize the steering angle of the MPC controller. The high computational complexity of the MPC controller was solved within the specified time constraints. The steering angle was calculated by the Stanley controller, and then served as the input into the MPC controller. The control quantities were modified using an exponential form. The model simplification was fully met the real-time control requirements of the navigation system. Finally, an inertial measurement unit (IMU) and satellite positioning module were employed to obtain the real-time pose information of the platform. The field path tracking experiments were conducted using a soil sampling platform. According to the straight path Tr1 and curved path Tr2 as the reference paths, tracking performance tests were conducted at a platform speed of 0.8 m/s for the MPC-Stanley controller, pure pursuit (PP) controller, and proportional integral derivative (PID) controller on both straight and curved trajectories. The results demonstrated that the MPC-Stanley controller was achieved in the best performance of the path tracking. The state variables of the system were predicted using the motion model. The MPC-Stanley controller was effectively resolved the overshoot and oscillation in the PID controller, indicating the superior robustness, compared with the PP controller. Subsequently, the tracking error tests were conducted for the MPC-Stanley controller, PP controller, and PID controller on the straight trajectory Tr1 and curved trajectory Tr2 at four speeds: 0.8, 1.6, 2.4, and 3.2 m/s. Test results indicated that the MPC-Stanley controller was achieved in the average absolute deviation, the maximum absolute deviation, and standard deviation of 3.1, 4.7 and 1.2 cm, respectively, during Tr1 straight-line path tracking at all four speeds, which were reduced by 43.6%, 43.4%, and 14.3%, respectively compared with the PP controller, and 20.5%, 23.0%, and 7.7% respectively, compared with the PID controller. In the MPC-Stanley controller, the dynamic model was fully leveraged to avoid the large system errors that caused by the absence of the angular control in the PP controller. The MPC-Stanley controller demonstrated the more stable performance during path Tr1 tracking, compared with the PID controller. The MPC-Stanley controller was achieved in the average absolute deviation, maximum absolute deviation, and standard deviation of 3.9, 6.6, and 1.5 cm, respectively, during curved path Tr2 tracking, which were reduced by 80.2%, 79.8%, and 85.7% over the PP controller, and 93.0%, 89.8%, and 90.5% over the PID controller. The MPC-Stanley controller can be expected to enable the adaptive parameter tuning using system inputs and outputs, delivering the superior control performance. The path-tracking was effectively enhanced the tracking accuracy of the soil sampling platform. Furthermore, the framework can be extended universally applicable to various agricultural platforms with the structures similar to the soil sampling platform. The finding can also provide a technical reference for the high-precision navigation in the field.

     

/

返回文章
返回