Research On Path Tracking Method For Intelligent Harvester Based On Model Predictive Control

Intelligent agriculture and precision agriculture are the development trends of agriculture in China.The intelligent combine harvests are easy to sideslip when working in the field.The steering control system of the harvester is serious lagging,which affects the harvester path tracking precision.In order to improve the accuracy and stability of path tracking for heavy combine harvesters in the field,a path tracking algorithm for heavy combine harvesters are studied.A path tracking algorithm based on Model Predictive Control(MPC)is proposed in view of the characteristics and working environment of large combine harvesters.Simulation experiments were designed to verify the effectiveness and performance of the proposed algorithm.According to the working environment,a path tracking system for heavy combine harvester is built.Experiments demonstrate that the path tracking system for heavy combine harvest performance well in the field.The main research contents of this paper are as follows:(1)The main causes of the steering control difficulty,control delay serious and hysteresis serious of heavy combine harvester are analyzed.The kinematics model and the discrete linear control system model of the intelligent combine harvester are established,the objective function of the model prediction controller is designed according to the control system model,and the objective function is transformed into a linear quadratic programming problem to calculate the expected steering angle of the harvester.In order to improve the adaptive capability of the control method,the influence of the weight matrix,prediction time domain and control time domain on the path tracking algorithm of the harvester is studied.Simulation results show that the proposed model prediction controller can improve the path tracking accuracy of harvesters.(2)A method to overcome the negative influence of sideslip under the kinematics model is studied.In the kinematics model,the judgment method of sideslip of harvester is studied.The estimation method of equivalent sideslip angle is studied.The expected steering angle is compensated using equivalent sideslip angle when sideslip occurs.Simulation results show that the proposed sideslip compensation method can improve the robustness of the path tracking system of the harvester.(3)The path tracking method of intelligent combine harvester based on MPC is verified.The path tracking system of intelligent harvester is built,including lower computer and upper computer.The position and attitude acquired module and steering control module of the harvester are designed based on STM32.The upper computer uses C++/QT to program the path tracking control software of the harvester,which mainly realizes the function of path planning and calculation of expected direction.Experiments show that the established harvester path tracking system can work stably in the field,and the mean value of lateral error of path tracking is 2.56 cm.