Research On Path Tracking And Steering Control Of Driverless Tractor

With the popularization of information technology and mechanization technology,precision agriculture technology has gradually developed.The automatic navigation technology of driverless tractor is an important part of intelligent agricultural machinery.Path tracking and steering control,as one of the key technologies of tractor automatic navigation,has become a research hotspot of researchers in recent years.Based on the research platform of HT-1804 F tractor,this paper studies the path tracking control and steering control of driverless tractor.First,on the basis of consulting domestic and foreign tractor automatic navigation products and related literature,the key technologies and methods used in path tracking control and steering control of driverless tractor are compared and analyzed;the existing problems and shortcomings of current technologies and methods are described.Secondly,this part studies the structure and principle of the path tracking and steering control system of the driverless tractor,and according to the basic requirements of the path tracking control of the tractor and the two degree of freedom dynamic model of the vehicle,establishes the tractor path lateral dynamic model based on preview,and studies the positioning coordinate conversion and tire model.Once again,the structural characteristics and working principle of the tractor steering system are studied.On the premise of not affecting the normal operation of the tractor's original full hydraulic steering system,a set of automatic hydraulic steering system is designed using three position four-way proportional reversing valve and other solenoid valves.Then,the transfer function relationship among the electromagnetic proportional directional valve,steering cylinder and steering wheel angle is established;at the same time,according to the electromagnetic proportional directional valve And the characteristics of the steering system,design an automatic steering control algorithm based on PID,and take the step signal and sine signal as the input,through MATLAB / Simulink software simulation,verify the feasibility of the designed automatic steering system.From then on,based on t analysis of the characteristics of tractor path tracking control,according to the tractor path lateral dynamics model based on preview,the lateral deviation sliding mode controller and heading deviation sliding mode controller are designed respectively by adopting the robust sliding mode control method.At the same time,the approach law parameters in the controllers are adaptively adjusted by using the fuzzy control method The lateral deviation sliding mode controller and the heading deviation sliding mode controller can get steering angle ?1 and ?2 respectively,which are combined to get steering angle ?.Based on MATLAB/Simulink and Car Sim simulation software,a joint simulation platform is established to simulate whether there is a fuzzy approach law,semi-circular turning and pear turning operation paths.The results show that the designed sliding mode controller based on the fuzzy approach law can track various operation paths stably and accurately.Finally,the test platform of HT-1804 F tractor is built,which is equipped with high precision positioning equipment,angular displacement sensor,automatic steering system and control equipment.After the calibration and debugging of each equipment,the test conditions of curve path tracking and pear shape path tracking are designed according to the field operation.The test results show that he designed control algorithm can make the tractor track the pear shaped work path stably,the maximum tracking error is 0.23 m,and the straight-line tracking error is within 0.076 m,which meets the accuracy requirements of precision operation.