基于MPC-Stanley的土壤采样平台路径跟踪方法

    Path tracking method of soil sampling platform based on 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对控制量进行了修正。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、4.2和1.2 cm,相比于PP控制器分别提高了43.6%、43.4%和14.3%,相比于PID控制器分别提高了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控制器分别提高了80.2%、79.8%和85.7%,相比于PID控制器分别提高了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: To address the limitations of poor path tracking performance and low tracking accuracy during the autonomous navigation of soil sampling platforms, this study proposes a path tracking method for soil sampling platforms based on MPC-Stanley. Firstly, a navigation system hardware architecture was designed for the soil sampling platform, and a control scheme for the navigation system was formulated. Secondly, a kinematic model was constructed using a bicycle model for kinematic modeling. Subsequently, model predictive control (MPC) was selected as the path tracking controller, deriving the control processes for both the MPC and Stanley controllers. To address the MPC controller’s high computational complexity and difficulty in solving within specified time constraints, the Stanley controller was employed to optimize the MPC controller’s steering angle. The steering angle calculated by the Stanley controller serves as input to the MPC controller. To meet the real-time control requirements of the navigation system, the control quantities were modified using an exponential form, achieving model simplification. Finally, using a soil sampling platform as the control object, an inertial measurement unit (IMU) and satellite positioning module were employed to obtain real-time pose information of the platform, conducting field path tracking experiments. Using straight path Tr1 and curved path Tr2 as 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 tests demonstrated that the MPC-Stanley controller achieved the best path tracking performance. By predicting the system’s state variables based on the motion model, the MPC-Stanley controller effectively resolved the overshoot and oscillation issues observed in the PID controller, exhibiting superior robustness compared to the PP controller. Subsequently, 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 indicate that during Tr1 straight-line path tracking, the MPC-Stanley controller achieved average absolute deviation, maximum absolute deviation, and standard deviation of 3.1 cm, 4.2 cm, and 1.2 cm respectively across all four speeds. Compared to the PP controller, these values improved by 43.6%, 43.4%, and 14.3% respectively. Compared to the PID controller, improvements were 20.5%, 23.0%, and 7.7% respectively. The MPC-Stanley controller fully leveraged the advantages of the dynamic model, avoiding the large system errors caused by the PP controller’s lack of angular control. Compared to the PID controller, the MPC-Stanley controller demonstrated more stable performance during path Tr1 tracking. During curved path Tr2 tracking, the MPC-Stanley controller achieved average absolute deviation, maximum absolute deviation, and standard deviation of 3.9 cm, 6.6 cm, and 1.5 cm respectively across four velocity conditions. This represents improvements of 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 enables adaptive parameter tuning based on system inputs and outputs, delivering superior control performance. The path-tracking method designed in this paper effectively enhances the tracking accuracy of the soil sampling platform. Furthermore, this method is universally applicable to various agricultural operation platforms with structures similar to the soil sampling platform described herein, providing a technical reference for high-precision navigation operations in the field.

       

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