| Agriculture is the basic industry supporting the construction and development of the national economy.The automated driving system of unmanned agricultural machinery is an important technology facing precision agriculture,realizing agricultural modernization and measuring the comprehensive strength of the country.In particular,the stable and accurate path tracking control algorithm can improve the operation efficiency of agricultural machinery,relieve the manual labor,is the key to the automatic driving system of agricultural machinery.In this paper,the path tracking control system of Dongfanghong LX1104 four-wheel drive tractor in field operation is studied deeply as a controlled test platform.Based on the line-of-sight(LOS)guidance law,a stable and reliable path tracking control strategy for agricultural machinery was designed.The main content is the following three aspects:(1)Through the research on the overall architecture of path tracking control system,the lateral control model of agricultural machinery dynamics is established.Firstly,according to the vehicle body state information acquisition,front wheel steering control and other modules involved in the system,the mathematical modeling is carried out based on the vehicle dynamics theory,and then combined with the demand analysis and simplified system design of agricultural machinery path tracking control,a two degree of freedom lateral control model meeting the requirements of agricultural machinery path tracking system is established.(2)Combined with the dynamic control model of agricultural machinery,the design of line of sight guidance system in the process of path tracking is completed.Firstly,in order to improve the dynamic response and stability of path tracking,the line of sight guidance method is introduced and deeply studied in the system.Then,based on it,the forward-looking distance and switching line of sight circle radius in the guidance law are improved respectively,which further improves the flexibility and adaptability of the system.Finally,combined with the lateral dynamics control model,an agricultural machinery path tracking line of sight guidance system is designed.The reliability of the system is verified by the simulation of two different working conditions of straight-line and broken line guidance.(3)A path tracking lateral sliding mode control system is designed based on the strategy of line of sight guidance system.Firstly,in order to enhance the robustness and accuracy of the system,the extended state observer was designed for the sideside angle of the vehicle center of mass and external disturbance respectively,to provide accurate feedback compensation for the control system and verify its rationality by simulation.Then,in order to solve the chattering problem and improve the practical application value of sliding mode control system,considering the uncertainty of the internal model of the system and the physical limitations of the actuator input in practice,this paper designs a sliding mode controller based on fuzzy logic system and input saturation compensation on the basis of traditional sliding mode theory.Finally,compared with traditional sliding mode controller,the superior performance of the designed controller is verified,which can bring stable and accurate control input to the system.(4)Based on the design of line of sight guidance system and lateral sliding mode control system,the theoretical and engineering application of the complete agricultural machinery path tracking system is verified.Firstly,using Carsim/Simulink joint simulation platform,according to the above design,a path tracking system based on line of sight guidance method and sliding mode control is built,and the simulation comparison is carried out under the conditions of crosswind disturbance and no crosswind disturbance respectively,which comprehensively verifies the theoretical application feasibility of the system;Then,the path tracking system algorithm is applied to the driverless system of Dongfanghong LX1104 tractor through programming development,and its navigation and positioning,attitude system,angle sensor and electronic steering equipment are modified according to the control requirements,so as to build a complete real vehicle test platform.Finally,two different working conditions of dry field and muddy field are selected for field experiments.The results show that the agricultural machinery can complete the on-line tracking process in about 15 s,and the horizontal deviation of on-line path tracking can be basically kept within ± 5cm.It shows that the sliding mode control strategy of path tracking system based on line of sight guidance method studied in this paper can meet the requirements of route tracking accuracy of agricultural machinery field operation,It accords with the standard of automatic driving system for unmanned agriculture machinery in precision agriculture. |
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